Yep, I think the real original alternator was truly rated at 55-65 Amps, depending on the year (67-69) and the load based on options.

I'm using a 100-amp and have no electrical problems or load issues when running the VERY LARGE elec fan and other things non-stock (CD player in the glove box, alarm systerm, etc).

One thing for sure, if your BATT voltage goes to 12 or below with all these things turned on, then you are drawing more than the system can reproduce.

Battery voltage should always be well above 12 (mine stays above 13) at all times even with a strong load. Unless of course I kill the battery due to leaving lights on, CD on, etc, which I'm known to do.

Yes, its a 12-VOLT system, but a solid battery and system will push 12.5 to 14.5 volts at all times easily. In my humble opinion of course.